The present invention is in the field of electronic sensors and is specifically directed to apparatus and a method for sensing events from a remote location using a time sequence of images of an area in which the events occur.
Sensing the presence or absence of a person or an object at a specified location is a problem which occurs in many fields. In the field of security, for example, it may be desirable to know whether an individual has entered a restricted area or whether a guard who is supposed to be covering the area is in a proper position to do so.
In commercial fields, such as banking, it may be desirable to know how many tellers are on duty, how many customers are waiting to be served by the tellers and the average amount of time customers are spending with each teller. Information of this type is useful for employee scheduling and for informing customers, who are entering the bank, of how long they can expect to wait.
In an office environment, it may be desirable to know when a worker starts and completes a task or to gather data on tasks being performed by a large number of workers.
Currently, problems of this type are addressed in one of two ways. In security systems, frame based video motion detectors are often employed to sound an alarm when motion is detected in or near a restricted area. An exemplary system of this type is described in U.S. Pat. No. 4,737,847 entitled "ABNORMALITY SUPERVISING SYSTEM." The apparatus described in this reference monitors changes in luminance in a video image from frame to frame to detect motion in a monitored area. The monitored area can be divided into subareas having different alarm levels. Detected motion in one subarea, for example, on a sidewalk outside of a building can be ignored while motion in another subarea, for example, near a ground-floor window of the building, can cause an audible alarm to be sounded. In this patent, the various subareas are defined by an operator using a light-pen on a reference image.
While a system of this type may be suitable for surveillance applications, it is not appropriate for commercial applications due to the large amount of image data which would need to be processed. Accordingly, other types of systems have been used in commercial environments. One type of system, manufactured by Camtron, Inc. is designed for use in a banking environment. This system uses a network of sensors, including ultrasonic motion detectors, light-photodiode combinations and manually operated switches to determine if a teller is present at each teller's station, if a customer is present in front of the teller's station and the length of the queue of customers waiting to be served.
A system of this type may be subject to errors causing it to give inaccurate data. For example, if the fact that a teller is at his station is indicated to the system by the teller turning on a switch, and the teller forgets to turn off the switch when he or she leaves, the system may erroneously believe that the teller's station is still occupied. Also, the number of customers in the queue may be miscounted if this number is determined by counting the number of times that a beam of light directed at photodiode is interrupted. This count may be inaccurate if, for example, a person crosses the beam more than once or if the interruptions caused by two people overlap so that only one interruption is counted.